9424200994 Rev N 91Breaker Failure (50BF) ProtectionThe breaker failure (50BF) element provides protection and security for the power system against failureof the monitored breaker.Element logic connections are made on the BESTlogic™Plus screen in BESTCOMSPlus® and elementoperational settings are configured on the Breaker Fail (50BF) settings screen in BESTCOMSPlus. Asummary of the logic inputs and outputs and operational settings appears at the end of this chapter.BESTCOMSPlus Navigation Path: Settings Explorer, Protection, Current, Breaker Fail (50BF)HMI Navigation Path: Settings Explorer, Protection, Settings Group x (where x = 0 to 3), CurrentProtection, Breaker Fail 50BFElement OperationThe 50BF element monitors the current to determine whether or not current continues to flow into afaulted circuit after a circuit breaker has been directed to interrupt the circuit. In the event that currentcontinues to flow into the faulted circuit (after a defined period of time has elapsed sufficient for thebreaker to have interrupted the current), then the circuit breaker is considered to have failed, and stepsmust be initiated to trip the next set of breakers upstream in the power system. Breaker failure protectionmay be applied to any portion of the power system where failure of a circuit breaker to operate properlycould result in severe system damage or instability.Contact SensingBefore any relay output can occur, there must first be an initiating signal from external contacts. Twopossible initiating signals are either the 52 Breaker Fail Initiate (52BFI) signal or the 50 Breaker FailInitiate (50BFI) signal. Contact sensing circuitry allows the BE1-11g to monitor external contacts for thepresence of these signals.Logic to start the breaker failure timer via the 52BFI input is provided with breaker status supervision.Both the breaker status and the 52 BFI logic input must be true for the 52BFI logic input to cause a tripcondition. Information on setting up the breaker status logic can be found in the Breaker Monitoringchapter.Control TimerThe control timer provides a window of opportunity for a breaker failure output. It improves dependabilityby sealing in the initiate request to prevent stopping of a breaker failure timing if the tripping relay dropsout prematurely. The control timer is initiated by a 50BFI signal. Upon sensing the 50BFI transition from a0 to 1 state, the control timer seals in the 50BFI signal for the duration of the Control Timer setting. If thecontrol timer expires and the 50BFI signal is still present, an alarm signal occurs. A control timer setting ofzero (0) disables the control timer seal-in function allowing the control timer to follow the 50BFI input.ReTrip and TripPhase and neutral fault detectors monitor current in the phases and the ground current input. At least oneof these fault detectors must be picked up to start the breaker failure delay timer.The adjustable delay timer allows current to decay after the breaker is tripped. The delay timer is initiatedwhen either the 52BFI input or the 50BFI input becomes true. When both signals are false, the breakerdelay timer is stopped.ReTripThe ReTrip output is true when the delay timer is actively timing. The delay timer can be stopped by eitherthe fast current detector or the Block logic input being asserted. In BESTlogicPlus, the ReTrip output canbe connected to other logic elements to annunciate the condition, control other elements in logic, andstart the fault recorder (logic element FAULTTRIG).BE1-11g Breaker Failure (50BF) Protection
